1. Field
The present disclosure generally relates to composite materials, and deals more particularly with a method and apparatus for impregnating a continuous fiber reinforcement with a matrix material.
2. Background
Composite structures may be fabricated using composite build materials such as strips of preimpregnated fiber reinforcement (prepreg) that are applied over a supporting tool by automated fiber placement (AFP) machines. The prepreg used in automated fiber placement comprise a resin such as an epoxy that is reinforced with fiber such as carbon fibers. In some applications, however, where the structure is subjected to high temperatures, it may be necessary to use composite build materials such as ceramic matrix composites (CMCs). In addition to their ability to withstand high temperatures without degradation, CMCs are desirable for certain applications because of their light weight and resistance to corrosion.
CMCs typically comprise a ceramic matrix material such as a glass, a glass-ceramic or a crystalline ceramic in which refractory inorganic fibers are held. In one known process, CMCs are produced by preparing a liquid suspension of the ceramic matrix material in powdered form, and then immersing the inorganic fibers in the suspension. The suspension comprises a solvent such as water or an organic liquid as the carrier for the ceramic powders. In one variant of this process, known as slurry infiltration, the reinforcing fibers are passed through a ceramic slurry which penetrates the porous structure formed by the fibers. The driving force of the infiltration is largely capillary effect, but may be enhanced by vacuum or pressure. After the fibers have been infiltrated with the suspension, solvent is removed by evaporation. The materials discussed above are challenging to process and difficult to convert into build materials that are well-suited for high-volume production using techniques such as automated layup of prepreg.
Accordingly, there is a need for a method and apparatus for fabricating CMC build materials such as CMC prepregs. There is also a need for a method and apparatus as described above which are capable of producing continuous strips of CMC prepreg that may be used by AFP machines to automate the layup of CMC structures.